What is the estimated number of believers for roman catholicism?

Answer 1

There are approximately 1.2 Billion members of The Catholic Church. There are various "rites" within The Catholic Church (i.e., Eastern, Marian, Coptic, Armenian, etc.). The largest "rite" in The Catholic Church is the Latin Rite. I suppose one might distinguish them as Roman Catholics but the term "Roman Catholic" is not one that The Catholic Church assigns to herself. Technically, there is no such thing as "Roman Catholicism" except, perhaps, to the degree that all Catholics accept the successor of St. Peter (the pope, 1st Bishop of Rome) as the Vicar of Christ on earth. That's true regardless of whether a Catholic is an Eastern Rite Catholic or Coptic or Latin Rite, etc. There is also substantial scriptural (NT) and historical evidence that St. Peter was the 1st pope (Bishop of Rome). He was then succeeded by Linus, Cletus, Clement, Sixtus, etc., down to the current pope, Benedict XXIII. Non-Catholics will assign the term "Roman Catholic" to The Catholic Church for their own theological reasons & purposes but The Catholic Church does not recognize that term -- Roman Catholic -- as one that is legitimate or accurate. On another level, all Christians are members of the "catholic"/universal Church of Christ. But not all Christians are members of The Catholic Church. It's a little complicated and can be confusing sometimes.